The present invention is directed to an adapter bracket that can be connected to an existing conventional gate valve to convert it to a fire safety valve, for wireline operations and the like.
A wellhead tree on an offshore platform is equipped with a gate valve in which the piston-like valve actuator biases the valve to the closed position by means of a spring acting against the lower surface of the actuator piston head. Pneumatic pressure engages the opposite or upper surface of the piston to overcome the biasing spring and hold the valve in the open position. In the event of a well fire, power to the compressor is cut off and the biasing spring automatically shuts the valve curtailing the flow of well fluids thereby preventing an uncontrolled continuous flow of fuel to the fire.
On an offshore platform, temporary "blips" in power (momentary blackouts) are not uncommon. Such a blip shutting down the compressor and automatically closing the gate valve can, at times, be more than a nuisance. One such time, is during the performance of routine maintenance or well testing using conventional wireline techniques. A temporary power outage closing the gate valve severs the wireline, dropping the tool being employed, along with several thousand feet of wireline, downhole. In addition to the damage to the tool, additional expense will be incurred in fishing the wireline and tool out of the wellbore resulting in both the cost associated with the manhours of labor and that resulting from the hours of lost well production mounting as the clock runs.
In order to avoid such expensive fishing expeditions, it was not an uncommon practice to mechanically disable the biasing spring (i.e., to jam the actuator open) during wireline operations to guard against the possibility of a temporary power outage. Such a practice is obviously unsafe and represents a significant gamble that a fire will not occur during the time when the valve is jammed open.
In response to customer reaction to this problem, valve manufacturers began manufacturing a "fire safety valve" that enabled the valve to be held open by a cap over the end of the actuator rod. This cap had a portion made of fusible plastic material which, in the event of a fire, melted allowing the valve to close. While these modified valves solve the problem for future installations, the problem of the existing in-place conventional gate valves remains. The prospects of replacing the in-place valves with the more expensive fire safety valves, particularly for large producers with a significant number of wellheads, are not good, particularly in today's economy. A less expensive means of safely preventing wireline cutting is needed.
The present invention satisfactorily fills this need. An adapter plate which has an externally threaded cylinder projecting from one side thereof is externally clamped to the actuator housing for a conventional gate valve. This adapter permits the conventional gate valve to be converted to a fire safety valve by the attachment of the identical fusible cap that is utilized in conjunction with the recently developed fire safety valves. The adapter of the present invention does not require any modification to be made to the existing valve actuator but can be clamped onto the outside of the existing actuator and, if desired, can be shifted from wellhead to wellhead as each receives a wireline workover, log test, etc., as required. Further, tests have shown that the adapter bracket can withstand extended periods of exposure to pressures as high as 10,000 psi without failing.
Other features, advantages and characteristics of the present invention will become apparent after a reading of the following detailed description of the invention.